This is using new bronze valve guides. We have the machine shop hone
them for 0.004" clearance between the valve stem and the guide (the
valve stem outside diameter is 0.004" less than the valve guide
inside diameter for its entire length). I'd have to dig out the
manual to see what the stock spec is, but I KNOW that (in racing,
anyway), 0.002" will stick valves - generally the exhaust, but the
intakes will stick too, and 0.003" is marginal. It seems a little
sloppy with 0.004" and we generally have to convince the machine shop
that we really mean it. Even with this clearance, if we really
overheat the motor we'll start to see sticky / bent valves.
If you have pushrods mysteriously popping out from under the rocker
arms, sticky valves is the primary culprit (as is an adjuster that
backed WAY out).
There are some things you can do to force more water to the rear of
the engine (reduce the hole diameter for the water through the head
gasket in the forward cylinders), but we run this clearance regardless.
My understanding is that iron guides expand less so can use a bit
less clearance, but I have no personal experience with those.
- Tony Drews
At 01:58 PM 9/19/2009, Alan Myers wrote:
>Hi,
>
>
>
>Tony, maybe you can clarify a little on what you've been doing when
>setting up your engines... And perhaps I can add a bit
>about?a?possible?reason?this happens...
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